Glycol ethers, the products of reaction between ethylene oxide and an alcohol have been a well-known industrial chemical since the 1930s, but it is only since the 1970s that they began to be extensively used. Glycol ethers are hydrocarbons with both alcohol and ether functional groups, making them a highly versatile and widely-used class of industrial chemicals with a wide range of applications in many different product areas. Because they are polar molecules and possess the strong hydrogen bonding characteristics of the alcohol and ether functional groups, glycol ethers are miscible in water and in organic solvents. This dual functionality gives glycol ethers the unique ability to solubilize many types of chemicals, so glycol ethers are commonly used as solvents in industrial processes and manufacturing as well as thinner and rheology modifiers in water-based paints, coatings and cleaning solutions. Glycol ethers that comprise longer chain alcohols are miscible in and can solubilize nonpolar organic compounds and oils and so can serve in many other industrial applications such as colorants, plasticizers, and lubricants.
Historically, methanol was most often selected for reaction with ethylene oxide and the resulting mono- and diethylene glycol methyl ethers occupied the largest segment of the glycol ether market. However, in recent years, ethylene glycol butyl ether, made from the reaction of butanol and ethylene oxide, and its higher molecular weight homologues have become of particular interest for their use as solvents, industrial chemicals and chemical intermediates. In fact, production of this butyl family of glycol ethers has risen much faster than many other families of glycol ethers since the 1970s, displacing other solvent products for both environmental and health reasons. (See P. de Ketttenis, Historic and Current use of glycol ethers: a picture of change, Toxicology Letters, 156, 5-11 (2005). doi:10.1016j.toxlet.2003.12.076).
In view of the increasing importance of these glycol ether chemical families it has become necessary to ensure continued process development and refinement to maximize process economics and efficiency. For example, historically it was taught that glycol ether manufacturing processes should be designed and operated to maximize the making of mono- and diethylene glycol ether and not higher molecular weight products. Thus, U.S. Pat. No. 3,935,279 teaches that while mono- and diethylene glycol ether had economic value and their production should be maximized, higher molecular weight homologues such as tri- and tetraethylene glycol ether were essentially waste products to be disposed of.
However, as glycol ether products increase in importance, it has become less and less desirable to simply dispose of a significant amount of manufactured product especially as these higher molecular weight homologues such as tri- and tetra-ethylene glycol ether have value and are particularly useful in high boiling point applications. Thus, improvements to the process to enhance higher molecular weight glycol ether recovery would not only increase the recovery of heavy products but also improve the overall yield of the process itself.
Accordingly, there is a continuing need in the art for a glycol ether process, in which a suitable amount of higher molecular weight homologues, especially tetraethylene glycol ethers, are recovered during the process.